| From abaeb7d0202c383661fa97514d1f671756e2994c Mon Sep 17 00:00:00 2001 |
| From: Michael Kelley <mikelley@microsoft.com> |
| Date: Mon, 1 Apr 2019 16:10:52 +0000 |
| Subject: scsi: storvsc: Fix calculation of sub-channel count |
| |
| [ Upstream commit 382e06d11e075a40b4094b6ef809f8d4bcc7ab2a ] |
| |
| When the number of sub-channels offered by Hyper-V is >= the number of CPUs |
| in the VM, calculate the correct number of sub-channels. The current code |
| produces one too many. |
| |
| This scenario arises only when the number of CPUs is artificially |
| restricted (for example, with maxcpus=<n> on the kernel boot line), because |
| Hyper-V normally offers a sub-channel count < number of CPUs. While the |
| current code doesn't break, the extra sub-channel is unbalanced across the |
| CPUs (for example, a total of 5 channels on a VM with 4 CPUs). |
| |
| Signed-off-by: Michael Kelley <mikelley@microsoft.com> |
| Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com> |
| Reviewed-by: Long Li <longli@microsoft.com> |
| Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> |
| Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org> |
| --- |
| drivers/scsi/storvsc_drv.c | 13 +++++++++++-- |
| 1 file changed, 11 insertions(+), 2 deletions(-) |
| |
| diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c |
| index 84380bae20f1..e186743033f4 100644 |
| --- a/drivers/scsi/storvsc_drv.c |
| +++ b/drivers/scsi/storvsc_drv.c |
| @@ -668,13 +668,22 @@ static void handle_multichannel_storage(struct hv_device *device, int max_chns) |
| { |
| struct device *dev = &device->device; |
| struct storvsc_device *stor_device; |
| - int num_cpus = num_online_cpus(); |
| int num_sc; |
| struct storvsc_cmd_request *request; |
| struct vstor_packet *vstor_packet; |
| int ret, t; |
| |
| - num_sc = ((max_chns > num_cpus) ? num_cpus : max_chns); |
| + /* |
| + * If the number of CPUs is artificially restricted, such as |
| + * with maxcpus=1 on the kernel boot line, Hyper-V could offer |
| + * sub-channels >= the number of CPUs. These sub-channels |
| + * should not be created. The primary channel is already created |
| + * and assigned to one CPU, so check against # CPUs - 1. |
| + */ |
| + num_sc = min((int)(num_online_cpus() - 1), max_chns); |
| + if (!num_sc) |
| + return; |
| + |
| stor_device = get_out_stor_device(device); |
| if (!stor_device) |
| return; |
| -- |
| 2.20.1 |
| |
